EP1712351B1 - Composite elastic nonwoven fabric and method for its preparation - Google Patents

Abstract

In an elastic composite non-woven (A) comprising a first layer (L1) of stretchable material of polypropylene fibers bonded to a second layer (L2) of elastic material, the elastic material is a propylene-ethylene copolymer, (L2) at least partially penetrates into (L1) and the elastic material of (L2) encloses part of the fibers of (L1). An independent claim is included for the production of (A), by applying the propylene-ethylene copolymer in molten form to the (L1), the viscosity and impinging speed of the melt being such that the elastic copolymer material at least partially permeates into (L1) and encloses part of the fibers of (L1).

Description

The invention relates to a composite elastic nonwoven fabric having a first layer of a stretchable polypropylene fabric and having a second layer of elastic material bonded to the first layer. The invention also relates to a method for producing such a composite nonwoven fabric.

The need for elastic composite nonwovens is generally due to the fact that elastic fabrics usually feel sticky or plastic like and do not have the typical textile feel. It has therefore been in the past to laminate these elastic fabrics with nonwovens, to obtain in this way a composite elastic nonwoven fabric having on its outer side a textile handle, but overall also has elastic properties.

A generic method is also in the EP 0 740 714 described. The composite nonwoven fabric described therein has at least one material layer with multipolymeric fibers of a blend of propylene polymer and polyethylene. These fibers are consolidated by means of a plurality of bonds to form a coherent, stretchable nonwoven fabric. A second layer of material, which is either stretchable or elastic, is connected to the stretchable first layer of nonwoven fabric. This composite can be done both with and without an adhesive, ie all-surface or interrupted by thermal or chemical means or by Kalanderprintbonding or adhesive application. A disadvantage of the known nonwoven composite is that additional measures for connecting the individual layers must be made in order to avoid separation of the layers.

From the DE 102 12 842 A1 In addition, a nonwoven material with elastic properties is known, which either consists of a multi-layer composite with at least one layer with fibers of an elastic polymer, or of a homogeneous fiber mixture in which a portion of the fibers consists of an elastic polymer. In the elastic layer of such a multi-layer composite, besides the elastic fibers, bicomponent fibers or melt-blown fibers may be contained. As the elastic polymer, polyurethane, a polystyrene block copolymer, copolymers of colypropylene and polyethylene, or elastomeric polypropylene can be used. The other layers may be polyolefin spunbond layers, needle felt layers, or polyolefin meltblown layers which are subjected to stretching to them to give certain elastic properties. The individual layers of the multi-layer structure are connected to one another by needling, water jet needling or by thermobonding.

Such a method is for example in the US-A-3,575,782 described. A similar procedure is also in the DE 103 04 370 disclosed.

Common to all these known composite nonwovens is that the individual layers of the laminates can be separated again, which makes it necessary to join the individual layers either by means of adhesive or thermobonding method or mechanically.

The object of the present invention is therefore to provide an elastic composite nonwoven fabric which has the typical textile handle on at least one outer surface, in which the individual layers can no longer be separated, without an additional adhesive or another joining technique being used here got to.

This object is achieved with respect to the composite nonwoven fabric in that the elastic material consists of fibers of a propylene-ethylene copolymer mixture, wherein the fibers of the second layer penetrate into the first layer and the fibers of the elastic material of the second layer a part of the fibers encase the first layer. With regard to the method, the object is achieved in that as an elastic material fibers of a propylene-ethylene copolymer mixture are applied in a molten state to the first layer, wherein the viscosity and the impact velocity of the melt is selected so that the fibers of the elastic Material at least partially penetrate into the first layer and encase a portion of the fibers of the first layer.

This solution ensures that not, as usual, both layers are more or less on each other, but that the second layer penetrates into the first layer and thus gives the first layer elastic properties, but without affecting the textile handle this first layer , On the other hand, the advantage of this method is that by selecting the amount of elastic material it is possible to adjust the permeability of the composite elastic nonwoven fabric. It makes use of the property that the propylene-ethylene copolymer, as far as it is in the form of a Melt impinges on the polypropylene fibers of the first layer, not only sheathed these fibers, but forms with appropriate amount and process management, even between the fibers swimming-skin-like sails. In this way, with a corresponding amount of composite nonwoven fabric even largely liquid impermeable, but water vapor permeable be set.

As a first layer is in principle any textile fabric suitable, which also provides a sufficient material depth for the penetration of the melt in addition to a corresponding elasticity.
Particularly preferred, but not limited to, is the use of staple fiber nonwovens.
Staple fiber webs have, due to a Vliezahl of protruding fiber ends, not only the desired textile handle; they are in contrast to other materials also voluminous and therefore give the material of the second, elastic layer better the opportunity to penetrate into the first layer.

Carded staple fiber webs which are suitable in the context of this invention are preferably made of fibers in the titanium range of 1.7 dtex to 6.7 dtex, the solidification can be done by means of thermal consolidation using hot air, but also using a Kalanderprägung.

If the calendering process is chosen, a low solidification surface and solidification point density should be chosen so as to provide the most stretchable layer with good porosity for the penetrating polymer.

That the basis weight of the first layer between 50g / m ² and 15g / m ^2, preferably at 22 g / m ² is still more preferred.

It is further preferred if the polypropylene fibers of the first layer are so-called "skin" fibers. These are those fibers in which the outermost layer of the fiber, the so-called "skin", has a substantially higher melt flow index (MFI) than the underlying layers. This increased melt flow index at the outer layer of the fibers improves the intermeshing of the elastic material of the second layer into the outer regions of the fibers of the first layer and therefore ensures the composite adhesion.

For the second layer, an elastomeric material is preferred, which consists of a mixture of two polymer components, wherein the first polymer component is a propylene-ethylene copolymer having a propylene content of at least 80 wt.%, And having a melting point of below 70 ° C, and wherein the second polymer component is a stereoregular, isotactic polypropylene having a melting point of greater than 130 ° C, wherein the proportion of the second polymer component is less than 25% by weight.

Such a propylene-ethylene copolymer mixture is disclosed in U.S.P. EP 1 177 337 B1 of Exxon Mobile Chemical Patents Inc. The product is commercially available under the trade name "Vista Maxx".

With regard to the method, it is furthermore advantageous if the second layer is introduced into the first layer by a melt-blown process. In this process, the fibers of the elastic material penetrate deeply into the first layer and encase a majority of the fibers of the first layer, whereby the total thickness of the composite nonwoven fabric hardly increases compared to the thickness of the first layer. In particular, it is preferred if the basis weight of the second layer between 80 g / m ² and 30g / m ^2, preferably 50g / m ^2. It should be noted here that the second layer is actually no longer a layer, since the material of the second layer predominantly penetrates into the first layer and connects inseparably to the first layer, which elastically binds it rather than a second layer form. This effect can be enhanced by a subsequent heat treatment. A suitable heat treatment has proven to be carried out at a temperature which lies below the melting temperature of the polymers which form the first layer and, moreover, also below the melting point of the second polymer component within the second layer but above the melting point of the first polymer component the second location, lies.

By means of this heat treatment, furthermore, a comparison of the crystalline structure within the second layer is achieved.

If desired, it is preferable to apply a further layer to the composite nonwoven during this heat treatment.

Fig. 1

einen schematischen Verfahrensablauf zum Herstellen eines erfindungsgemäßen Verbundvliesstoffs,

Fig. 2

in einer vergrößerten Darstellung einen Schnitt durch ein Verbundvliesstoff, und

Fig. 3

das Detail III aus der Darstellung in Fig. 2 in einer weiteren Vergrößerung, und

Fig. 4

das Detail IV aus der Darstellung in Fig. 2 in einer noch stärkeren Vergrößerung.

In the following the invention will be explained in more detail with reference to embodiments. Show it:

Fig. 1

a schematic process sequence for producing a composite nonwoven fabric according to the invention,

Fig. 2

in an enlarged view a section through a composite nonwoven fabric, and

Fig. 3

the detail III from the illustration in Fig. 2 in a further enlargement, and

Fig. 4

the detail IV from the illustration in Fig. 2 in an even greater magnification.

First, a staple fiber fleece 2 is unrolled from the roll 1 as a carrier fleece. The staple fiber fleece 2 is a polypropylene fleece with a thickness of 0.37 mm and a basis weight of 22 g / m ² .

The fleece is bonded on a point-by-point basis and thus retains the stretchability and porosity required for the desired end product. The term extensibility in the context of this invention describes the property of the first layer to be deformed with little force up to a maximum elongation of up to 300% in the direction of use necessary in later use.

Through the nozzle 3, a propylene-ethylene copolymer mixture is applied in the melt-blown process on the carrier fleece, which is commercially available under the name "Vista Maxx" from the company Exxon Mobile. The composition in detail is in the EP 1 177 337 B1 described. This material is an elastic copolymer with a low melting point and high heat capacity. In the process, care must be taken that the fibers emerging from the spinneret 3 still impinge on the carrier web 2 in the form of a melt. This is especially in the described meltblown process by a small distance of the nozzle tip of the spinneret. 3 reaches the carrier fleece 2. As a result, the propylene-ethylene copolymer penetrates deeply into the carrier layer 2, as will be described in more detail below. At the same time, the fibers of the carrier fleece 2 are sheathed.

The process is controlled so that about 50g / m ^{2 of} the propylene-ethylene copolymer are applied to the carrier web 2. However, the thickness of the total web behind the spinneret 3 only increases from 0.37 mm to 0.41 mm due to the penetration into the first fiber layer.

The porosity of the composite nonwoven fabric thus obtained changes so as to significantly increase the number of pores as compared with the original layer 1, and at the same time reduce the pore sizes. Pore sizes of less than 80 μm have proven suitable. This ensures an increase in barrier properties, in terms of resistance to water pressure in mm water column, up to a water column of 200 mm, while maintaining the breathability, expressed here as air permeability in l / (m ² · sec) and water vapor passage in g of water vapor per m ² and day. Results for the example described above can be found in Table 1.

The result of this process is a stretchable, elastic composite nonwoven fabric in which the outer layers have a textile handle, but the individual layers can no longer be separated from each other and in which the layers are indissolubly connected without the intervention of an adhesive or other measures.

Fig. 2 shows here the layer structure of the composite web in detail. With A and B are the thicknesses of the two staple fiber webs 2, which form the outer layers of the composite nonwoven fabric designated. C denotes the thickness of the elastic center layer of the propylene-ethylene copolymer. It can be seen that the middle layer penetrates both staple fiber fleece layers, ie that the material of the middle layer penetrates deep into the staple fiber fleece 2.

This is better from the electron micrograph Fig. 3 to recognize.

The individual fibers protruding in the upper part of the image belong to the staple fiber fleece. In the middle and lower part of the picture are the individual fibers of the Stapelfaservlieses by the material of the elastic layer, namely encased by the propylene-ethylene copolymer. In addition, between the fibers of the staple fiber fleece spun web-like threads which connect the individual fibers of the staple fiber fleece transversely.

In Fig. 4 in which a further magnification is shown under the scanning electron microscope, these filaments are to be recognized as well as the fact that the individual fibers of the staple fiber fleece are covered by the propylene-ethylene copolymer.

In a further preferred embodiment, the applied, elastic layer is heated in step 4 and held at the melting temperature, shortly before the roll 5 another staple fiber fleece made of polypropylene is placed and pressed by means of a calender. The composite web produced in this way is then wound onto the roll 7.

Composite nonwoven fabrics made as described above can now be used in a variety of applications.

Thus, due to the elasticity, the use in the fit of personal hygiene products influencing components is possible.

The achieved in the product according to the invention combination of the properties of elasticity, barrier effect and breathability also opens up the possibility of using such a composite nonwoven fabric as an elastic liquid-repellent barrier layer on the body-facing surface of a personal hygiene article, which ensures the comfort even during intense exercise. This requirement profile also coincides with the requirements in the field of medical associations. Here, the use of skin-friendly, polyolefinic basic components has an advantageous effect. Table: Production parameters of the material according to the invention Composite 2-ply Composite 2-ply Composite 3-ply parameter standard unit without heat treatment with heat treatment with heat treatment grammage EN 29073-1 g / m ² 77.9 78.6 100.3 Tear force along EN 29073-3 N / 5 cm 38.6 46.6 101.53 Tear force across EN 29073-3 N / 5 cm 12.9 15.4 26.58 Fmax - stretching longitudinally EN 29073-3 % 65 74.7 69.8 Fmax - stretching across EN 29073-3 % 135.7 156.5 203.4 Elasticity transverse (as permanent elongation after elongation to 100% and relief) EN 29073-3 % 21 15 15 Water vapor transmission JIS K 7129-1992 g / (m ² d) 688 624 480 water column EN 20811 mm 78 150 196 Air permeability (200Pa) EN-ISO 9237 l / m ² / s 215 206 190 pore size Description below microns 40 77 67

Pore size: Determination of the largest pore according to the following principle
The test method takes advantage of the physical context that the pressure to be applied, which is required to force air bubbles through a sample soaked in liquid, is inversely proportional to the size of the corresponding pore.

The corresponding equation is: $$\mathrm{d}\mathrm{=}\frac{\mathrm{4}\mathrm{\times }\mathrm{\sigma }\mathrm{\times }\cos \left(\mathrm{a}\right)\mathrm{\times }\mathrm{10}}{\mathrm{p}}$$

σ:

Oberflächenspannung der Benetzungsflüssigkeit [mN/m]

a:

Randwinkel am Übergang Flüssigkeit / Stoff (aus Vereinfachungsgründen wird cos (a) =1 angesetzt)

p:

Prüfdruck (mbar)

d:

Porendurchmesser (µm)

Prüfflüssigkeit: Ethanol (96%). Die Qualität des verwendeten Alkohols muss vermerkt werden, die Oberflächenspannung muss bekannt sein. Prüfklima: Probenvorbereitung nach DIN 50 014: 23/50 Anzahl der Proben: 10 Probengröße: Durchmesser 56mm, Prüfgerät: geeignetes Messgerät, mit geeignetem Druckaufnehmer Prüfablauf: Die zu untersuchenden Proben werden in Ethanol getränkt bzw. mit Ethanol befeuchtet, eingespannt und mit einer Ethanolschicht von ca. 5 mm beschichtet. Über das Feinventil wird der Prüfdruck sehr langsam gesteigert (nicht schneller als 1 mbar Anstieg in 2 Sekunden). Beim Aufkommen der ersten Luftblase wird der zugehörige Wert der Porengröße in µm als "größte Pore" notiert. Der zweite Messpunkt wird festgehalten, wenn die gesamte Oberfläche der Probe mit Luftblasen bedeckt ist. Es ist der Messpunkt "viele Poren". Werden verarbeitete Papierproben geprüft, wird unterschieden in größte Poren im Faltenbereich und größter Pore in der Fläche. Ergebnis: Mittelwerte und Streuung, Angabe der Werte in der Einheit µm Here mean:

σ:

Surface tension of the wetting liquid [mN / m]

a:

Edge angle at the transition liquid / material (for reasons of simplification, cos (a) = 1 is used)

p:

Test pressure (mbar)

d:

Pore diameter (μm)

test fluid: Ethanol (96%). The quality of the alcohol used must be noted, the surface tension must be known. Test conditions: Sample preparation according to DIN 50 014: 23/50 Number of samples: 10 Sample size: Diameter 56mm, tester: suitable measuring device, with suitable pressure transducer Test sequence: The samples to be examined are soaked in ethanol or moistened with ethanol, clamped and coated with an ethanol layer of about 5 mm. The test pressure is increased very slowly via the fine valve (not faster than 1 mbar increase in 2 seconds). At the appearance of the first bubble, the corresponding value of the pore size in μm is recorded as the "largest pore". The second measuring point is recorded when the entire surface of the sample is covered with air bubbles. It is the measuring point "many pores". If processed paper samples are tested, a distinction is made between the largest pores in the fold area and the largest pore in the area. Result: Mean values and scattering, specifying the values in the unit μm

Claims (18)

1. Composite elastic nonwoven fabric having a first layer consisting of an extensible fabric made from polypropylene fibres and having a second layer consisting of an elastic material bonded to the first layer, characterised in that the elastic material consists of fibres of a propylene-ethylene copolymer mixture, the fibres of the second layer (8) penetrating into the first layer (2) and the fibres of the elastic material of the second layer sheathing part of the fibres of the first layer.
2. Composite nonwoven fabric according to claim 1, characterised in that the first layer consists of a staple fibre nonwoven fabric.
3. Composite nonwoven fabric according to one of claims 1 or 2, characterised in that the weight per unit area of the first layer is between 50 g/m² and 15 g/m², preferably 22 g/m².
4. Composite nonwoven fabric according to one of claims 1 to 3, characterised in that the polypropylene fibres of the first layer have an outer coat having a substantially higher melt flow index than the coats below it.
5. Composite nonwoven fabric according to one of claims 1 to 4, characterised in that the elastic material of the second layer, in other words the propylene-ethylene copolymer mixture, consists of a mixture of two polymer components, the first polymer component being a propylene-ethylene copolymer having a propylene content of at least 80 wt.% and a melting point below 70°C and the second polymer component being a stereoregular, isotactic polypropylene having a melting point above 130°C, the content of the second polymer component in the mixture being moreover below 25 wt.%.
6. Composite nonwoven fabric according to one of claims 1 to 5, characterised in that the elastic second layer is covered by a third layer made from a polypropylene staple fibre nonwoven fabric, the second layer at least partly penetrating the third layer.
7. Composite nonwoven fabric according to one of claims 1 to 6, characterised in that the average pore size of the largest pore in the composite nonwoven fabric is less than 8 0 µm.
8. Composite nonwoven fabric according to one of claims 1 to 7, characterised in that the water vapour permeability of the composite nonwoven fabric is at least 400 l/(m² 24h).
9. Composite nonwoven fabric according to one of claims 1 to 8, characterised in that it has a water pressure resistance of at least 150 mm water column.
10. Composite nonwoven fabric according to one of claims 1 to 9, characterised in that the permanent elongation in the load direction of the composite nonwoven fabric is less than 20%.
11. Composite nonwoven fabric according to one of claims 1 to 10, characterised in that the extensibility of the nonwoven substrate in the load direction is at least 200%.
12. Composite nonwoven fabric according to one of claims 1 to 11, characterised in that the density of the composite material is at least twice as high as the density of the nonwoven substrate.
13. Composite nonwoven fabric according to one of claims 1 to 12, characterised in that the second layer is covered by a third layer consisting of a polypropylene stable fibre nonwoven fabric, the fibres of the third layer being at least partly sheathed by the material of the second layer.
14. Method for the preparation of a composite nonwoven fabric according to one of claims 1 to 13, characterised in that fibres of a propylene-ethylene copolymer mixture in the molten state are applied to a first layer consisting of an extensible fabric made from polypropylene fibres as the elastic material, the viscosity and the impact velocity of the melt being chosen such that the fibres of the elastic material at least partly penetrate into the first layer and sheath part of the fibres of the first layer.
15. Method according to claim 14, characterised in that the material of the second layer is introduced into the first layer by a melt blown process.
16. Method according to claim 14 or 15, characterised in that the weight per unit area of the second layer is between 80 g/m² and 30 g/m², preferably 50 g/m².
17. Method according to one of claims 14 to 16, characterised in that the composite nonwoven fabric is subjected to a heat treatment at a temperature below the melting point of the material of the bottom layer and the melting point of the second polymer component of the second layer and above the melting point of the first polymer component of the second layer.
18. Method according to one of claims 14 to 17, characterised in that a third layer consisting of a polypropylene staple fibre nonwoven fabric is applied to the second layer whilst the fibres of the second layer are still in the molten state.

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